HyperText Transfer Protocol (“HTTP”) is a stateless protocol. Web servers and Web browsers support “cookies”, which provide a state needed for a Web site. A cookie is a text file that a Web server sends to a Web browser, and that the Web browser returns to the Web server. The cookie contains state information relating to the Web browser. The Web server uses the state information to restore a previous state of a Web page on the browser.
Proxy servers or user preferences set in a Web browser can prevent the use of cookies. A technique for maintaining a Web browser state, which does not use cookies, is called “URL rewriting”. As background, each HTTP command contains a uniform resource locator (“URL”) and optionally some parameters. URL rewriting appends a session identifier (“ID”) to every URL contained in a Web page. The session ID identifies a session and thus state information associated with that session. The session ID may be returned to the Web server when a user clicks on any link in the Web page. The Web server uses the session ID to restore the state of the Web page to the browser.
Thus, both cookies and URL rewriting may be used to preserve a state of a Web page during browsing. But, if multiple browser windows are opened, the state is shared between windows. As a result, actions in one window will affect the other windows. This is because a Web browser can support cookies from a Web server, but not related to individual windows. URL rewriting has a similar limitation, because it is concerned with tracking a state of a user, not the state of a browser window.
By way of example, two Web browser windows may be opened to compare stock prices. Each window may display a stock “ticker”, which includes charts and date ranges. In conventional systems, changing a chart type or date range in one window will result in the same changes being made in another window when that other window is updated.
Having actions in one window affect states of other windows is not always desirable.